Production of titanium sesquioxide



Patented June 22, 1954 UNITED STATES PTENT OFFICE PRODUCTION OF TITANIUM SESQUIOXIDE N Drawing.

Application May 24, 1952,

Serial No. 289,880

Claims. 1

This invention relates to the production of titanium sesquioxide and, more particularly, to a method of producing titanium sesquioxide substantially uncontaminated by other oxides of titanium.

There has been described and used heretofore a method of producing titanium monoxide by heating an intimate mixture of titanium carbide and titanium dioxide to a temperature within the range of 1300 to 1750 C. In the course of an investigation of the chemistry and mechanism of this reaction, we have discovered that the titanium monoxide is formed by two successive reaction stages, the first stage being the conversion of titanium carbide to titanium sesquioxide and the second stage comprising the conversion of the titanium sesquioxide to titanium monoxide. Although our investigation showed that the two reaction stage take place simultaneously throughout the reaction mass at temperatures Within the range of 1300 to 1750 C., and that titanium sesquioxide is formed simultaneously with titanium monoxide within the reaction mass, we have discovered that the first reaction can be made to proceed to the substantial exclusion of the second reaction provided a lower temperature range is used than that heretofore required in the aforementioned method of producing titanium monoxide. Thus, We have found that if a mixture of the titanium carbide and titanium dioxide is heated to a temperature within the range of 1000 to 1200 C. in an inert atmosphere, substantially pure titanium sesquioxide is produced. When this titanium sesquioxide is subsequently reacted with a further quantity of titanium carbide, the resulting titanium monoxide is less contaminated with higher oxides of titanium than when the monoxide is produced in the aforementioned single stage process.

Accordingly, our novel method of producing titanium sesquioxide comprises forming an intimate mixture of finely divided titanium carbide and titanium dioxide, the amount of titanium carbide being at least stoichiometrically equivalent to that of the titanium dioxide, heating the mixture to a temperature within the range of about 1000 to 1200 C. in an inert atmosphere,

removing the resulting evolved carbon monoxide, 1

of the titanium sesquioxide with the impurities otherwise associated with the titanium carbide. The impurities normally present in significant amounts in titanium carbide of commercial grade comprise iron and graphite. The iron can be elfectively removed by grinding the titanium carbide to a particle size of minus 325 mesh (Tyler Standard), and preferably to a particle size of about one micron or smaller, adding hydrochloric acid to an aqueous slurry of the finely ground carbide, and subsequently Washing the carbide to remove entrained chlorides. The removal of graphite from the titanium carbide is not essential if the titanium sesquioxide produced therefrom is to be reacted with a further quantity of titanium carbide for the production of titanium monoxide, but the graphite may be an undesirable impurity if carried over to the titanium sesquioxide to be used for other purposes. If the graphite need be removed, this can be effected by dispersing the titanium carbide in a slightly alkaline aqueous medium and separating the graphite by conventional froth flotation procedure. Inasmuch as the treatment of commercial grade titanium carbide for the removal of contaminated iron is generally resorted to, the resulting finely divided form of the purified titanium carbide is advantageous because it enhances its reactivity with the titanium dioxide.

The titanium dioxide which is reacted with titanium carbide in the practice of our invention should be of sufiicient purity to avoid contamination of the titanium sesquioxide product. Titanium dioxide such as that formed by hydrolysis from an aqueous acidic solution of a titanium salt may be used with particular advantage. Although such titanium dioxide is formed in the course of titania pigment production, the crystalline form, and hence the pigmentary quality, of the titanium dioxide is of no importance in the practice of our invention. Of course, the use of addition agents which are conventionally added in producing titanium dioxide pigments need not and should not be used in producing high purity titanium dioxide for use herein. For maximum reactivity with the titanium carbide, the titanium dioxide admixed therewith should also be in finely divided form, and in general it can be said that the substantially pure titanium dioxide which is suitable for the practice of our invention is readily available in commercial quantities in such finely divided form as to be adapted for admixture with the titanium carbide Without further treatment to reduce its particle size.

The admixture of the titanium carbide and the titanium dioxide is preferably carried out with suincient thoroughness to insure uniform distribution of both components throughout the mixture. Although intimacy of contact between the reactants is provided by such thorough mixing, we have found it to be further advisable to enhance the intimate contact of the titanium carbide and titanium dioxide particles by compressing the mixture. For example, we have obtained particularly eifective results by adding about 5 to by weight of water as a temporary binder for the mixture and by subsequently pelletizing the damp mixture under compressive pressures of 10 tons per square inch and higher. The resulting intimate contact is, we have found, conducive to substantially quantitative reaction between the titanium carbide and titanium dioxide.

Inasmuch as, in our process, the titanium carbide and titanium dioxide react substantially quantitatively in a manner which can be expressed by the equation TiC+5TiO2- 3Ti2O3+CO, the relative amounts of the reactants can be def initely specified. Thus, in order that the titanium sesquioxide be substantially free of contamination by unreacted titanium dioxide, the mixture should be composed of an amount of the titanium carbide at least stoichiometrically equivalent to that of the titanium dioxide. If the titanium sesquioxide is to be used for such purpose as, for example, a starting material in the production of other trivalent titanium compounds, it is generally advisable to use substantially stoichiometric quantities of the titanium carbide and titanium dioxide so that the final product will be composed substantially exclusively of titanium sesquioxicle. On the other hand, if the titanium sesquioxide is to be reacted with a further quantity of titanium carbide for the production of titanium monoxide, a portion or all of this further quantity of titanium carbide may be incorporated in the initial titanium carbidetitanium dioxide mixture. The aforementioned variation in the relative amounts of reactants which may be used in practicing our invention appears to have no significant eifect upon their reactivity at temperatures within the range which we have found to be important.

The temperatures which we have found to be conducive to the formation of titanium sesquioxide substantially uncontaminated by other titanium oxides pursuant to our invention lie within the range of about l000 to about 1200 C. Within this range, higher temperatures make possible the use of shorter reaction periods, but within the entire temperature range we have found that substantially complete conversion of the titanium carbide to titanium sesquioxide is effected within a maximum of about three hours. A reaction period of one to two hours is generally sufficient for complete reaction at temperatures approximating the upper limit of the useful temperature range. In any event, the proper duration of the reaction period may be ascertained by cessation of evolution of the single gaseous reaction product, carbon monoxide.

Under the aforementioned reaction conditions, the gaseous reaction product comprises carbon monoxide and the residual reaction product comprises titanium sesquioxide. The removal of the carbon monoxide from the reaction zone, and hence the progress of the reaction, is enhanced by the two procedures which we have found to be particularly useful in maintaining the desired inert atmosphere in the reaction zone. Thus, we have found it to be advisable either to sweep the reaction zone with a stream of inert gas or preferably to maintain active vacuum pumping conditions throughout the reaction period. Argon and helium are typical of useful inert gases, and vacuums cf the order of 10 millimeters of mercury or less are generally suitable for the practice of our invention, although we prefer to maintain vacuums of the order of to 100 microns of mercury in the reaction vessel.

The reaction vessel used in practicing our invention should, of course, be such as to prevent contamination of the reaction product. For example, molybdenum and Hastaloy may be used satisfactorily for the vessel which holds the reaction mass, and conventional furnace refractories may be used for those parts of the heating apparatus which are exposed merely to the gaseous product of the reaction. Thus, we have found that a molybdenum-lined graphite crucible positioned within an electrically heated furnace is particularly satisfactory equipment for either small or large scale operation.

The practice of our invention is illustrated by the following specific example in which a reaction mixture was prepared by thoroughly mixing together 80.0 parts of pigment grade titanium dioxide and 30.0 parts by Weight of pure titanium carbide. The mixture was then moistened with about 10% by weight of water and was pelleted under a pressure of about 10 tons per square inch. The pellets were charged to a molybdenum-lined graphite crucible in a vacuum furnace heated by induction. A vacuum of about 50 to microns of mercury was established and maintained throughout substantially all of the reaction period of 60 minutes during which the furnace temperature was maintained at 1200 C. At the conclusion of the reaction period the furnace was allowed to cool while the vacuum was maintained. The black residual reaction product removed from the cooled furnace was identified by X-ray analysis to be essentially titanium sesquioxide (TizOs) further containing a small amount of titanium monoxide (TiO) in solid solution in titanium carbide. The utility of the reaction product Was demonstrated by further heating this reaction product in the same furnace at the same vacuum for a period of minutes at 1550" C. The resulting residual reaction product was golden brown titanium monoxide, and X-ray analysis of the product showed it to be pure TiO.

It will be seen, accordingly, that the method of our invention is capable of producing titanium sesquioxide substantially uncontaminated by other compounds, particularly by other titanium oxides. Consequently, our method may be used advantageously in conjunction with various processes for producing other titanium compounds of high purity, one such process comprising the use of titanium sesquioxide for conversion of titanium carbide to titanium monoxide and the use of the latter as a starting material from which titanium metal may be produced by fused bath electrolysis. Accordingly, the expression recovering the residual titanium sesquioxide, as used herein and in the claims, includes recovering the sesquioxide as such as well as recovering it as a reactant which, in admixture with residual or extraneous titanium carbide, is converted to titanium monoxide in a subsequent heating operation carried out at a temperature substantially in excess of that used in producing the sesquioxide by the method of our invention.

We claim:

1. The method of producing titanium sesquioxide which comprises forming an intimate mixture of titanium carbide and titanium dioxide, the amount of titanium carbide being at least stoichiometrically equivalent to that of the titanium dioxide, heating the mixture to a temperature Within the range of about 1000 to 1200 C. in an inert atmosphere, removing the resulting evolved. carbon monoxide, and recovering the residual titanium sesquioxide,

2. The method of producing titanium sesquioxide which comprises forming a pelleted intimate mixture of titanium carbide and titanium dioxide, the amount of titanium carbide being at least stoichiometrically equivalent to that of the titanium dioxide, heating the mixture to a temperature within the range of about 1000 to 1200 C, in an inert atmosphere, removing the resulting evolved carbon monoxide, and recovering the residual titanium sesquioxide.

3. The method of producing titanium sesquioxide which comprises forming an intimate mixture of substantially stoichiometric amounts of titanium carbide and titanium dioxide, heating the mixture to a temperature within the range 6 of about 1000 to 1200 C. in an inert atmosphere, removing the resulting evolved carbon monoxide, and recovering the residual titanium sesquioxide.

4. The method of producing titanium sesquioxide which comprises forming a pelleted intimate mixture of substantially stoichiometric amounts of titanium carbide and titanium dioxide, heating the mixture to a temperature within the range of about 1000 to 1200 C. in an inert atmosphere, removing the resulting evolved carbon monoxide, and recovering the residual titanium sesquioxide.

5. The method of producing titanium sesquioxide which comprises forming an intimate mixture of titanium carbide and titanium dioxide, the amount of titanium carbide being stoichiometrically in excess of that of the titanium dioxide, heating the mixture to a temperature Within the range of about l000 to 1200 C. in an inert atmosphere, removing the resulting evolved carbon monoxide, and recovering the residual titaniumv sesquioxide product.

No references cited. 

1. THE METHOD OF PRODUCING TITANIUM SESQUIOXIDE WHICH COMRPISES FORMING AN INTIMATE MIXTURE OF TITANIUM CARBIDE AND TITANIUM DIOXIDE, THE AMOUNT OF TITANIUM CARBIDE BEING AT LEAST STOICHIOMETRICALLY EQUIVALENT TO THAT OF THE TITANIUM DIOXIDE, HEATING THE MIXTURE TO A TEMPERATURE WITHIN THE RANGE OF ABOUT 1000* TO 1200* C. IN AN INERT ATMOSPHERE, REMOVING THE RESULTING EVOLVED CARBON MONOXIDE, AND RECOVERING THE RESIDUAL TITANIUM SESQUIOXIDE. 